Amorphous InSnZnO Thin-Film Transistor Voltage-Mode Active Pixel Sensor Circuits for Indirect X-Ray Imagers

An amorphous indium-tin-zinc-oxide thin-film transistor (a-ITZO TFT)-based voltage-mode active pixel sensor (V-APS) is discussed, for the first time, in this paper. The a-ITZO TFT shows superior electrical characteristics, including a high field-effect mobility (μEFF> 30 cm2/V · s), a steep subthreshold slope (SSOFF-14A), that are suitable for applications such as X-ray imagers. The proposed V-APS is based on the topilluminated organic photodiode (OPD) or amorphous silicon p+-i-n+photodiode (a-Si+-i-n+PD). Simulation results indicate that, in contrast with common source V-APS, source follower (SF) V-APS is more desirable for X-ray imagers due to its better linearity property. The OPD or the a-Si p+-i-n+PD does not affect the voltage gain of SF V-APS. But the PDs have different influences on charge-to-voltage conversion gain. The impact of PD capacitances and dark saturation currents on detectable quantities of electrons is also investigated. The influence of the TFT threshold voltage shift on circuit performance, sensitivity, and noise analysis of SF V-APS is discussed.